A CSX freight train blasts through high snow at a crossing in Silver Spring, Maryland, in a February 13, 2014 file photo.Gary Cameron/Files

(Reuters) - Former Canadian Pacific Chief Executive Hunter Harrison is in advanced talks to team up with a former Pershing Square Capital partner, seeking to shake up rival railroad CSX Corp (CSX.O), according to a person familiar with the matter.

Harrison on Wednesday announced his early departure from Canadian Pacific (CP.TO), the railway company he led after activist fund Pershing Square tossed out the previous CEO in a 2012 proxy fight.

The Pershing Square partner who led the Canadian Pacific investment was Paul Hilal, who last year left the firm to start his own fund.

Hilal's fund, Mantle Ridge LP, has raised more than $1 billion for a single investment, according to a person familiar with the matter, with investors committed to locking up their money for five years.

The investment is expected to be aimed at CSX, with Harrison seen as playing a similar leadership role to help turn the company around as he did at Canadian Pacific, the person said.

Harrison confirmed to The Wall Street Journal on Wednesday that he and Hilal were finalizing a partnership.